What Is Your Sedimentation Rate?

The sedimentation rate -- or “sed rate,” for short -- is a blood test that checks for inflammation in your body. It’s one clue for your doctor that you might have a disease linked to inflammation, like arthritis or cancer.

The sed rate test measures how fast red blood cells fall to the bottom of a tube. Inflammation creates proteins that make red blood cells fall more quickly.

Another name for this test is erythrocyte sedimentation rate (ESR). Red blood cells are called erythrocytes. Sedimentation is the process by which they fall to the bottom of the tube.

Why You Might Get a Sed Rate

Your doctor might order the sed rate test if you have symptoms like these:

  • Headaches
  • Stiff joints
  • Pain in your shoulders, neck, or pelvis
  • Appetite loss
  • Weight loss without trying

The sed rate test can be part of the process of discovering if you have one of these conditions:

You might also get this test once you've started treatment for one of these conditions. The sed rate can help your doctor see how well your body is responding to treatment.

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Taking the Blood Sample

You don’t need to do anything special to prepare. It's just a basic blood test.

Let your doctor know what medicines (and supplements) you take before you have the test. Certain drugs can affect the results. Also let your doctor know if you are pregnant or are having your period.

A nurse or other health care provider will take a sample of your blood, usually from a vein in your arm. He will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then he’ll clean the area with an antiseptic, and place a needle into your vein. Your blood will collect into a vial or tube.

The process should only take a couple of minutes. Afterward, you’ll get a piece of gauze and a bandage over the area to stop the bleeding.

You may feel a slight sting as your blood is drawn. Afterward, you may have a small bruise. You might feel feel dizzy and sore, and there might be some bleeding.

The Results and What They Mean

Your sample will go to a lab. You should have the results in 1 or 2 hours.

A lab technician will place your red blood cells into a tall, thin tube and check how far they fall in 1 hour. When you have inflammation in your body, abnormal proteins in your blood make red blood cells form into clumps. These clumps are heavy, so they fall to the bottom of the tube more quickly than single blood cells.

The faster the blood cells sink, the more inflammation you have in your body.

The sed rate test reports in millimeters (mm) the distance between the clear liquid (plasma) at the top of the tube and your red blood cells after 1 hour. The normal range is:

  • 0 to 15 mm/hour in men younger than 50
  • 0 to 20 mm/hour in men older than 50
  • 0 to 20 mm/hour in women younger than 50
  • 0 to 30 mm/hour for women older than 50

A high sed rate is a sign you have a disease that causes inflammation in your body.

Some conditions and medicines can affect the speed at which red blood cells fall, and they may affect your test results. These include:

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Other Tests You May Need

The sed rate test can only tell your doctor that you have inflammation somewhere in your body. It can't show where the inflammation is or what caused it. Your doctor will use the sed rate test together with other tests of inflammation, such as C-reactive protein, to make a diagnosis.

Talk to your doctor about the results of your sed rate test, and any other tests you have. Make sure you understand what the results mean, and how they'll affect your treatment.

WebMD Medical Reference Reviewed by William Blahd, MD on January 20, 2017

Sources

SOURCES:

American Association for Clinical Chemistry: "ESR."

Mayo Clinic: "Sed rate (erythrocyte sedimentation rate): How you prepare," "Overview," "Results," "Why it's done."

National Heart, Lung, and Blood Institute: "What to Expect With Blood Tests."

Nemours Foundation: "Blood Test: Erythrocyte Sedimentation Rate (ESR)."

University of Rochester Medical Center: "Erythrocyte Sedimentation Rate."

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